text:
How does thrust relate to horsepower on turbocharged engines?
Could someone please help me understand the difference between horsepower and thrust on turbocharged engines?  I believe I have a good understanding regarding the purpose and operation of a turbocharger, but what I don’t understand is why the overall performance goes down even when the turbocharger is capable of making max PSI below the rated “critical altitude”.  For example, if my turbocharger can produce 40” from sea level to 12,000 DA, why does my climb performance decrease with altitude?  40” will produce max horsepower from sea level to 12,000, but the performance charts clearly demonstrate a loss of climb performance between sea level and 12,000’ DA, and I just don’t understand why.  Thank you!

Assuming you are talking about a turbocharged propeller driven aircraft, your question
really makes it easy to explain as you have already identified the two parts of your power unit
that are affected by increasing altitude (thinner air).  The amount of air it can breath and the amount of thrust your prop can generate.
The turbo only takes care of the air breathing part, yes, it has as much power as at sea level
because to turbocharger can compress enough of the thin air to feed it. No problem there.
But the prop is still spinning thinner air, so it can not get the same "bite" as at lower altitudes
with out going to even higher RPMs.  So, when your RPMs max out due to engine limitations,
or even the tips going supersonic, that's it, no more thrust increase available.

The main issue is the sea level torque is available to the engine, but as density decreases the propeller blades are forced to operate at a higher and higher blade angle (higher and higher local angle of attack) to absorb the available torque, to keep the rpm at the speed set by the governor.  This takes the propeller blades out of their most efficient AOA range so that the thrust efficiency of the propeller declines somewhat as the air thins out.

Engine/prop combinations provide approximately a constant power into the airflow. (Jet engines proved approximately a constant thrust.)
Here are some links, if you’re interested in that relationship.
http://www.srmuniv.ac.in/sites/default/files/downloads
http://web.mit.edu/16.unified/www/SPRING/systems/Lab_Notes/airpower.pdf/class10-2012.pdf
http://www.dept.aoe.vt.edu/~lutze/AOE3104/climb.pdf
Power = force x velocity, so the power required from the engine to maintain level flight for a given operating condition is drag x speed. If the engine can put out that much power (with an efficiency term for loss in conversion) then you can maintain level flight. If the engine can put out more, then you can convert the excess power available into climb. If you hold drag fixed somehow but increase velocity, you have less power available to climb.
Note that the speed to get required power is your speed with respect to the fixed inertial frame of the air mass, and so is TAS not IAS.
Now your drag is a function of IAS. Your best rate of climb Vy is at a fixed IAS, so in a climb at Vy, you see the same drag no matter the altitude.
So as you go higher, the power required just to maintain level flight at Vy goes up since your TAS goes up for the same fixed IAS.
Your climb rate is going to be a function of the difference between power available from the engine (fixed, thanks to the magic of turbocharging) and power required for level flight (increasing as you go higher due to a higher TAS for the same IAS).
This leaves less excess power available to convert into the climb as you go higher.

Thrust is thrust, whether it comes from a rocket, a jet, or a propeller.  The propeller gives less thrust at a given RPM because the air is thinner.  The difference in TAS and IAS is actually an advantage at altitude, your drag is from IAS, your GROUND SPEED is TAS.  For a turbo, your power does not change (nor would it if the prop fell off the plane), but the efficiency of converting RPM to thrust drops in thinner air.  Eventually thrust drops to where you can only maintain IAS needed for level flight.  That's where the pilot needs more oxygen too.

Robert, there are too many references to back up my assertion that props are constant power while jets are constant thrust, but here is one. http://www.srmuniv.ac.in/sites/default/files/downloads . And another, equation 6 on page 1. http://web.mit.edu/16.unified/www/SPRING/systems/Lab_Notes/airpower.pdf/class10-2012.pdf .  And this one, page 2. http://www.dept.aoe.vt.edu/~lutze/AOE3104/climb.pdf

@ MikeY Well, the bridge over troubled waters is constant RPM.  Piston engines are unfortunately limited in RPM, but theoretically would provide more POWER (fuel burn per second) to spin the prop FASTER if RPM or SONIC BARRIER were not an issue.  Ways around rpm limitation include more blades, wider blades, damn the sound barrier, full speed ahead (noise regulations and Thunderscreetch in mind).  But jets pour that fuel in to get more POWER to turn their fans at higher altitudes, where greater TAS makes up for lower THRUST per gallon efficiency.  But power does not move the plane.

@RobertDiGiovanni: MikeY is right, fly faster and the same power means less thrust. If the propeller's solidity has been calculated with density at FL180 in mind (hint: If the critical height is FL180, the propeller should also keep up with converting that power to thrust), then density just means that blade lift coefficient goes up a bit, but thrust is not affected by the lower density.

@Peter Kampf MikeY answer is good, except for the notion that the power/thrust relationship is somehow different than jets.  It may be inaccurate to describe climbing ability on power, particularly in this case.  A good turbo could go up to 60,000 feet, and if he could reach out his window and put a 25 foot 8 bladed supersonic prop on there, he WOULD get to 60,000 feet at 2500 rpm.  RPM is the limiting factor with piston props, and in this case the prop craps out while the engine has more to give.  Actually, it may be you can't fly faster with the same power if there is less thrust.

And notice you make the wings bigger to get to higher altitudes too, if you must avoid the Mach barrier, which is at lower and lower IAS as you go up.  Smaller, faster wings may get through as well! Jets are capable of much higher RPM and supersonic compressor/fan speed.  They are not RPM limited nearly as much, are lighter, though less efficient, can go high.


text:
Where can I find reports of accidents/incindents happened on ground?
What international organization or website has the information on this topic?
I’m looking for reports, statistics and analyses of incidents and accidents (other than those involving aircraft) that occurred at work locations of an airline, airport, or handling agent involving passenger handling service departments with customer service facilitating passengers and baggage, i.e., ticketing and reservations, check-in counters, immigration control, duty free shops or other concessionaires, boarding gates, jetways or aircraft steps, shuttle bus for boarding or arriving, aircraft parking bays, baggage claim areas, baggage conveyor belts, and other such locations.
ICAO, IATA and ACI have the stats but they're all aircraft related only.

[to the downvoters, try to at least leave a comment to help a newcomer help understand]

What's the problem you're trying to solve?

It looks like you want to get statistics of incidents/accidents of all kinds in the limits of an extended airport area (extended because work locations of an airline are usually close to an airport, but not in the airport). And that worldwide. I'm afraid such completeness is not possible, e.g. shuttle bus collisions and duty free shop floodings are not registered using any standards, and maybe there are no requirements for that at all. To help you edit your question, you may want to use the chat.

If you're excluding aviation safety incidents (those that relate directly to the safe operation of an aircraft), then I am pretty confident in saying that there is no single international source of the information you're seeking.
Those stats will probably be held by insurance companies, and the workplace safety authority of the country or state where the airport is located.

Apart from anything else, what workplace (non-aviation) accidents are reportable differs from state to state. Even when the stats are held, they might only relate to staff and not customers. And of course they won't include most accidents that don't cause any personal injury.

source: Stack Exchange

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text:
What is the APU actually used for?
What are the actual uses of the APU? When is it used? When does it go off?

Using 747-100/200 aircraft at the two 747 carriers I flew for in the 1990s as an example, the specific uses (not in any particular order) were:

pneumatic power to start the engines
pneumatic power to run the air conditioning packs when the engines were not running.
electrical power on the ground, available regardless of whether the engines were running or not. Many aircraft can use APU electrical power inflight, 747-100/200s do not.
hydraulic power on the ground when the engines were not running via the pneumatic duct. I can't remember whether that could be done inflight.

Assuming that electrial and air was not available from a ground cart, the APU on a cold airplane would be turned on when the airplane was opened up and turned off after the engines were going.
Prior to landing, the APU would usually be turned on a few minutes before landing. It would be left on until a ground cart (if any) was hooked up or until the aircraft was vacated and closed up.
Other aircraft types and operators employ their own procedures, and their APU uses may differ.

Hi Terry.  I've often wondered if there are SOPs which leave the APU On for longer, for example until the end of the STAR or 10,000 feet.  My thinking is that in an emergency, having the APU already on would save time and increase options, Sully on the Hudson being an example.  Of course, fuel and component times are the compromises.

@Simon We had no such SOP, but I can well understand that they might have such these days. The 747, with four engines, each with a generator and two hydraulic pumps, has a lot of redundancy, and if an engine fails,  its pneumatically driven hydraulic pump will keep operating using air from the common pneumatic duct. Impossible to know, I think, how much lower the probability of losing all four engines to bird ingestion is than with only two engines.

In a nut-shell

Source, page 906

In Detail

Source, page 906
APU stands for auxiliary power unit.
It provides the aircraft electricity and bleed air. In german APU translates to "Hilfstriebwerk". This directly translated into english means "Helping engine". That's why some german speaking people think this is an additional engine to provide thrust for the aircraft. The APU does not produce any thrust when running. However, it can help the engines producing more thrust, when turned on.
The APU generates following power:

Pneumatic power
Electrical power
Hydraulic power (Indirectly)

The main uses for the APU are following:
Providing electricity at the gate, when no engines are running
At most airports, big enough to fit an aircraft equipped with an APU, there are GPU's (Ground Power Unit) available. A GPU is the same as an APU, but is on ground, connected with the aircraft.

Source
There is also the Air Start Unit, a ground based system providing pressure air and the Air Conditioning Unit, ground based as well and providing air conditioning.
However, if the airport isn't equipped with such units or there is another reason they can't be used, the APU can replace all of them.
It is providing the electricity for the plane and the bleed air for the packs (air conditioning) and the engine start.
But note: The above mentioned ground units, usually don't replace the APU if they are available. Because usually, the engines are started during pushback, there can't be a ground unit connected to the aircraft.
To answer your question for this part, when the APU goes on and off: It usually will be turned on before pushback, or if there is no GPU, upon entering the cabin. After all engines have started and are stabilized, the APU can be turned off.
Relieve the engines during take-off by using bleed-air from the APU
If full power is needed for the take-off, what is rare, the engine bleed can be turned off, as bleed air by the engines decreases power. That also means, no air conditioning. If the pilots want air conditioning during take-off, they can turn on the APU and use it's bleed air.
Providing electricity in-flight in case of engine-failure(s)
In case of an engine failure the APU is turned on, to assure the operation of all aircraft systems. The electrical power for the avionics and the hydraulic power to control the control surfaces.
Providing bleed-air to start the engines
All big jet aircraft are using pneumatic power to crank the engines. This can be done with the bleed air of the engine, the Air start unit on the ground or the APU. As mentioned above, engines are usually started during pushback, so the APU is mostly used to achieve this task.
Turning the APU on is also an item on the after landing checklist. As the APU needs some time to spool up as well, it is started after landing. When at the gate, the engines can be shut down directly. The APU just supplys electricity for the period between engine stop and connection of the GPU.

If you want to inform yourself deeper, you can look into the A320 FCOM. The APU section is starting at page 906.

A bleeds-off takeoff is hardly mandatory on most modern jets.  Most of the time, the APU is shut off before takeoff; shutting it off after takeoff happens in those uncommon cases where you do need a bleeds-off takeoff for performance.  Also, it is not normal to start the 2nd engine off of bleed air from the 1st engine -- that generates too much unnecessary jet blast.  Typically, the APU isn't shut off until all engines are running.

@RalphJ Thank you, I edited.

The APU, auxiliary power unit, is a generator that provides electrical power to important systems of an aircraft when the engines are not running. During normal operations, the APU is used on the ground just prior to engine start, and sometimes on the ground after landing. In unusual situations, such as an airborne engine failure, the aircrew can also choose to turn on the APU to ensure power is supplied to critical systems.

Additionally, pneumatic power -- i.e. bleed air.  This is used for air conditioning/pressurization, as well as starting engines (except in cases where the starter is electric -- mostly smaller engines).  The bleed air can also be used either on the ground or in flight, although there are often altitude limitations associated with using it to pressurize the airplane.  On a 737, for instance, the APU can be used up to 17,000' to pressurize, up to 10,000' to pressurize + supply electricity, or up to 41,000' for only its generator.

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Have any operational aircraft ever used over wing fuel tanks?
We are most familiar with under wing fuel tanks, has any operational aircraft ever used over wing fuel tanks?

What has the picture to do with your question, are you asking if this is an over wing fuel tank aircraft?

Both the Typhoon and English Electric Lightning used over the wing fuel tanks as standard equipment for many years. There may have been others.

English Electric Lightning

Typhoon (with conforming tanks)

Seen for Electric Lightening, but for the Typhoon? Seem more like conformal fuel tank(s)...

"Lightening" means "getting lighter". You mean "lightning": electrical discharge during storms.

The Typhoons fuel tanks in the picture are conformal fuel tanks, not overwing fuel tanks - the F-16 and F-15 also use conformal fuel tanks. The Typhoons conformal fuel tanks are also not in operation, they are still under development.

I was just thinking, for the many non-expert but who-doesn't-love-planes readers of this site .... you blokes should just include one word under photos like that, letting the reader know which photo is which. (Probably just "too obvious!" to you!)

Also, note that the name of the manufacturer is "English Electric". It's "the Lightning, made by English Electric", not "the Lightning, an English plane made by Electric."

@Moo: They're still over the wings, so they probably technically count.

Very true, @DavidRicherby, but as the fuel is consumed by the Lightning, the tanks are lightening... ;)

Early aircraft designs used gravity feed to supply the engines with fuel. All those designs had their tanks located above the wing, and in biplanes in the center of the upper wing. The picture below (source) shows an Etrich Taube with the cylindric fuel tank mounted above the fuselage.

The next application of overwing tanks were "Doppelreiter" fuel tanks (slipper fuel tanks) which were used on some German fighter airplanes in WW II. They were mounted above and behind the wing, and to everyone's surprise they had little impact on the top speed of the airplanes, and in case of the Me-309 helped to increase it slightly. They were the first practical application of Küchemann carrots and worked much like the flap track fairings of today's airliners.

FW-190 A with Doppelreiter tanks.

Great research! Very interesting.

@qqjkztd: Area ruling is the answer. At that time, nobody knew of it, so the effect cam as a surprise.

Any pics of the 309 with the tanks? There are none at the Wiki article linked...

@FreeMan Nope, lots of drawings and plastic models with those tanks on the web, but no original photos, I'm afraid. We still have to wait for someone to upload one.

Haz a sad. sniff

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text:
Why is the flight director at 9 degrees nose high when hitting TOGA?
Why is the flight director set to 9 degrees pitch up, when pressing the takeoff / go-around (TOGA) button? In all the jets I fly, this is the case and I would be curious to know if other jets set their pitch attitude to a different value.

curious to know if other jets set their pitch attitude to a different value.

747-100/200 aircraft didn't have a TOGA button to press, but at the two 747 carriers I flew for in the 1990s, the flight engineer filled out a data card for takeoff and later for landing that listed the pitch attitude target for takeoff and go-arounds, both for 3-engines and 4-engines. He/she looked up the values in tables in the QRH (Quick Reference Handbook), a copy of which each cockpit crewmember had. The card was placed against the instrument panel such that all three cockpit crew members could see it.
The target attitude depended not only upon the number of operating engines, but also engine type, aircraft weight, flap setting, and OAT. I just looked in my old QRH, and the lowest target I found was 9°, the highest was 19°. As I remember, typical actual operational values ran from 10° to 14°. Values higher than 14° were for very light weights and thus would be rarely used.
The 4-engine target pitch was generally 2° higher than the 3-engine pitch except that at very low weights, the difference was 3°.
Adherence to the target attitude was up to the flying pilot as he/she would be hand flying the airplane without flight director guidance.


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Why would a plane drop 14.000 ft mid flight?
Just noticed American Airlines flight 221 dropped 14.000 ft mid flight today. Curious, what could have caused this?
Here are the flight details.

Do you honestly believe the plane "dropped" 14,000 feet?

I looked up the flight on Flightradar24.com. The descent starts at 16:10 UTC and ends at 16:29 UTC, going from 38.000 feet to 24.000 feet. So, the aircraft descended 14.000 feet in 19 minutes.
14.000 divided by 19 makes roughly 750 feet per minute, which is a relatively normal descent rate for airliners.
The cause for this is probably an ATC instruction. The descent starts around 20 minutes ahead of the border of the U.S.A and ends directly in front of it (SSM VOR is the entry point to US Airspace).

Source
So, this is probably the cause for the descent: The pilots contacted the US controller around 20 minutes ahead of them entering US airspace. The controller then instructed the pilots to descent to 24.000 feet and reach this altitude at the SSM VOR. So, no uncontrolled drop there.

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text:
Where do aerodynamical contrails get their condensation nuclei from, when forming at high altitude?
On this website, it is explained how aerodynamical contrails form:

It’s formed by the reduction of pressure in the air as it moves over the wing.  When the pressure of a gas falls, then its temperature also falls (the same principle as is used by your refrigerator).  The reduced temperature cause small drops of water to condense, which then may freeze.  The (frozen) drops get larger as more water condenses on them.

Here is a photo of aerodynamical contrails forming at high altitude:

Source
As can be seen, the aerodynamic contrails start right at the wing. What I want to know is, where the oversaturated air condenses. "Normal" contrails coming from the engines use the soot from the engines as condensation nuclei. But what about the aerodynamic ones?
I think the water vapour condenses on the wing, but I need to know it for sure.

What you see is condensation due to a change in pressure. Pressure and temperature are related by the ideal gas law. Warmer air can hold more humidity, colder air holds less. It's usually seen with fighter jets, such as this one

Condensation in free air requires condensation nuclei, they probably exist high up in the atmosphere as can be seen by cloud formation at altitudes up to 13km.

So, that means, an aerodynamical contrail can only be seen, when the air is already full of condensation nuclei? And that's also what makes them so rare?

I'm saying you need condensation nuclei for condensation in free air, or a cold surface for water to form on top of it (a wing for example). As the airplane moves forward, the water slips off the surface and forms droplets.

It sounds plausible that the condensation nuclei are forming on the wing surface then blowing off. I suspected, though, that in the right conditions to form aerodynamic contrails, namely supercooled water vapor at sufficient vapor pressure, the contrails can form via homogeneous nucleation. I can’t find a number without wading through technical papers that are beyond me, but at some point the vortices can increase the local density to a point that the nuclei form spontaneously without the need for aerosols. But I can’t verify that.

If you look at your first pic of the fighter plane you see that the condensation is forming at quite a distance from the wing. So the wing is not contributing nucleation sites. The shock wave has altered local conditions sufficiently for homogeneous nucleation. ....or so I suggest.

I can see your explanation with the vortices being a factor in  droplet formation, but wouldn't condensation nuclei still be required?

For the first picture I don't really see that the condensation is forming at quite a distance from the wing. It just seems downstream of the leading edge.

It is worth noting that CCN are not strictly required for droplet formation, but without any you need around 400% saturation ($e/e_s$), while with the right kinds of CCN you can get away with ~70% saturation.  Phase change is complicated, and the droplet formation / evaporation is not symmetric, so it is quite feasible that CCN are already present but it isn't until pressure drop occurs that sufficient moisture saturation occurs for droplet formation and growth.

Condensation nuclei are abundant in the atmosphere. Sea salt particles, atmospheric mineral dust, and lots of different aerosols, including anthropogenic air pollution particles are always present, and serve as condensation nuclei. That's why clouds can form at all, and that's why your breath can condense in cold weather.
There is more info at https://www.e-education.psu.edu/meteo300/node/671

Welcome to Av.SE!


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Can I make an ILS-Approach when I am VFR?
When doing a VFR-Flight, the runway to land on is usually approached visually. However, I would like to do some ILS-Training but in VFR.

Is that possible?
If yes: What's the procedure? Do I have to include something in my flightplan? Do I have to notify the Approach/Tower-Controller? In VFR the control zone is approached via pre-defined entry points like Echo or Sierra. But then I can't do an ILS-Approach because there is usually no entry point on runway track.

This may be a dupe of this question or this one. In the US it's common to practice ILS approaches under VFR at both towered and non-towered airports, but only if you know what you're doing, i.e. you're already instrument rated, or training with an instructor.

Procedures do vary between countries, so please specify the jurisdiction which you would like the answer to address.  As it stands, it's too broad and impossible to answer for all countries in the world in one answer.

As a VFR pilot you are responsible for terrain avoidance and avoiding other aircraft. As long as the tower clears you for a straight-in approach, there is nothing to prevent you from flying the ILS. That being said, it is fairly difficult to watch for terrain and traffic while also watching the needles. If you do it, you should have a safety pilot along.

Related: https://aviation.stackexchange.com/q/88954/

Sure you can.  Just request to fly the approach using either radar vectors or initial approach fixes, if available.  The tower will usually comply and grant you the approach clearance, adding "maintain VFR" i.e. The approach should be flown under visual flight rules and you cannot use a view limiting device unless you have an appropriately rated safety pilot onboard with access to dual flight controls.
For non towered airports, you will need to listen for traffic in the area on the CTAF and provide position reports often for the benefit of other pilots in the pattern.
Flying practice instrument approaches in VFR is quite common and many pilots do this to maintain instrument proficiency.  It is also common for instrument rated pilots to file a local IFR flight plan to practice as well.


text:
How can the A320 receive 3 DME signals if it has only 2 DME receivers?
How can the A320 receive simultaneously 3 DME signals (VOR1 + VOR2 + ILS) if it has only 2 DME receivers (and antennas)?
Does it multiplex them in some way? If yes, does it mean if one DME receiver fails I can still get simultaneously 3 DME values?
There is a video that shows 3 DMEs tuned simultaneously: Airbus Cockpit Views | Episode #6 | PFD View Landing STN RWY22

VOR1 (DME1) being automatically re-tuned, followed shortly by VOR2 (DME2), plus the already tuned ILS

My FCOM says:
Each FMGC automatically uses its five DME frequencies as follows:

One DME frequency for display. It is possible to tune it manually or automatically.

Two DME frequencies in DME/DME mode for calculating the radio position of the aircraft. The FMGC automatically tunes these as a function of their best accuracy. The flight crew does not receive any indication that this process is happening.

One DME frequency automatically tuned for radio position. This occurs in the VOR/DME mode, when the DME/DME is not available and the flight crew complies with the conditions for a VOR/DME update. In this case, the VOR/DME that the flight crew uses for display, is identical to the VOR/DME navaid that the flight crew uses for computation of the radio position.

One DME frequency is connected to the ILS/DME.


text:
Why is TOGA thrust 'never' 100% N1?
The title is voluntarily the opposite of this question: Why isn´t TOGA thrust always 100% N1 or N2?.
I explain to you with an example: I'm looking to the FCOM of an A320 which states that the "maximum in normal operation N1" is 100%, and "the maximum N1 permitted" is 105%. But then, by looking at the THRUST RATINGS - MAXIMUM TAKEOFF page, where there is the table with altitude on the columns and OAT on the rows, the maximum value of N1 that I can find is 94.5%. Any other N1 table (climb/go around/etc.) has clearly lower values for N1. In A320 this value is enforced by the FADEC and cannot be exceeded.
So what's the point to have a 100%-105% N1 limits if the enforced N1 limit in TOGA can be at maximum 94.5%? Why not just set 100% as the RPM value of 94.5%? Or the 94.5% can be exceeded?
Clarification:
My question is not related to maximum thrust (which it doesn't correspond to maximum N1). I cannot publish the table, however it's the same of this table, but for another engine and for the maximum takeoff mode instead of maximum climb.
I reformulate the question in a more direct way:

Why FCOM says N1 can reach 100% and 105%, if then no N1 mode allows any N1 value over 94.5%?

@ymb1 The 100%/105% limitation is in the Limitation section (LIM-ENG) just below the THRUST SETTING/EGT LIMITS section. The engine is one of the new engines of the neo, the PW1100G

Actually I've just noticed the same in another old FCOM with CFM56 engines, the 3.01.70 operating limitations section states N1 max 104%, but the N1 takeoff table never go above 100.1%

PW1133G-JM which should be the most powerful version, but probably you are right: it is  derated by the operator configuration, like what you can do on CFM56-7B: http://nandang-smart.blogspot.com/2014/09/cfm56-7b-identification-plug.html

The thing you are missing is that for a jet engine, there is no fixed relationship between rotor speed and thrust. For a given  speed, the thrust depends on altitude and air temperature.
Therefore, there are separate limits on engine operation for maximum thrust and maximum rotor speeds.
If you are at a "hot and high" airfield like Nairobi (say 30C at 6,000 feet) you will be limited by the rotor speeds. On the other hand in Reykjavik (200ft and 0C maximum in winter) you will be limited by the maximum thrust when the rotor speeds are well below the maximum.
I couldn't find the table you referred to in an on-line copy of the FCOM, so no comment about the specific data you were looking at for the A320.

Yes, this is correct, but the purpose of the table is exactly to show the relation with temperature and altitude. This is an example: https://forums.x-plane.org/uploads/monthly_2020_04/tat23.jpg.a51bb67b46495d6e3299c89a1a7fa41e.jpg (not the FCOM I'm looking at, I cannot publish it, but it's the same table but for Takeoff and another engine) But I expect to see at least one value at 100% of N1 in the table of the TOGA power...

I clarified the question.


text:
Why is there a strip of uncontrolled airspace between Russia and Norway?
The airspace between Russia and Norway over the Barents Sea is an uncontrolled air space; no FIR is set.

Illustration taken from this document.
This area is like a corridor from the Scandinavian peninsula to the North Pole. It only requires several minutes by a heavy airliner to pass east-west.
Why is this relatively small area not controlled?

I'm gonna guess politics, but I'm eager to see what the answer is

Is it a mapping/projection issue, since you're trying to depict a 3D sphere onto a 2D page?

Details of the No FIR area
The area extends on 175,000 square kilometers:

From ≈70°N (Bodø FIR) to the North Pole.
From 30°E to ≈32°05'E, and to 35°E for a portion east of Svalbard archipelago.

VATSIM Murmansk sectors (ATC simulation). Source

Border dispute
This Barents Sea strip is of major importance, and has been subject to a dispute between Norway and Russia for 44 years. The reasons include:

This area has been the maritime border between East and West blocks during Cold War (the country is neutral, but still a founding member of the NATO).
Norway is a country with many resources coming from the sea (fish, oil, gas), the sea area controlled by the State is six times its land area.
The Barents Sea is a location with multiple oil and gas fields to be exploited. The large Shtokman gas field (label "5" below) discovered in 1988 happens to be in the vicinity, an agreement was signed between Norway and Russian Federation for the development of the field, but only in 2005:

Oil and Gas in the Barents Sea (red dots are gas fields). Source
The area encompasses the most direct potential route between Europe and the Pacific after the ice floe has melt down.

This dispute was closed when a new treaty entered in force on July 2011 with the border crossing the 175,000 square kilometers disputed region in the middle.

(Source: BBC)
While the border is now settled, responsibilities for air traffic control are still to be formally defined by international bodies.
Currently transiting flights have to be authorized by respective authorities before operating in this area, e.g. London-Tokyo flights using Arctica 1 route, noted B483 on first picture. In addition of commercial flights, the Arctic region is highly monitored by manned and unmanned aircraft.
ICAO and Eurocontrol status
ICAO wants to resolve this issue of missing FIR:

8.1 IATA brought the attention of the Group to a portion of airspace of unassigned responsibility, extending from the North Pole over the
  High Seas between Bodo Oceanic FIR, Sondrestrom FIR and Murmansk
  Oceanic FIR (Appendix E refers). Considering the increase d interest
  of establishing new ATS routes through that airspace, the Group agreed
  on the following Conclusion:
TRASAS Conclusion 2/4 – Airspace of Unassigned Responsibility over the
  Arctic Ocean
  That the ICAO Secretariat be invited to take the
  necessary actions to resolve the pending issues regarding the portions
  of airspace of unassigned responsibility extending over the High Seas
  between Bodo Oceanic FIR, Sondrestrom FIR and Murmansk Oceanic FIR

Source:
Report of the Second Meeting of the Trans-Regional Airspace and Supporting ATM Systems Steering Group (TRASAS/2) (Bangkok, Thailand, 18-19 March 2008)
There is a proposal under Eurocontrol auspices (proposal 95.012) to close the topic by Summer 2021:

FIR border realignment Murmansk FIR / Bodø FIR / Norway FIR:
Objective: To resolve the long-standing issue of the unallocated
  airspace (NO-FIR area) between Murmansk FIR and Bodø FIR / Norway FIR.

Source: European Route Network Improvement Plan 2019-2024
No aeronautical services
Flying in a no FIR area (when such territory is not forbidden to aircraft) means there is no information service provided from the ground. Flight information service consists on informing aircraft about meteorological events, known other aircraft position and intentions and aids availability. Other services are not available either: No alerting (search and rescue) and no ATC. The related airspace belongs to none of A, B, C, ..., G classes.
For those who want to know more about FIR and Oceanic Control Area, see Who manages International Airspace Traffic?
No FIR areas in general
Regarding the existence of "No FIR" areas:

3) FIRs have not been established for a few areas in the world.
  These are commonly called uncontrolled information regions or “no
  man’s land.” The largest of these areas is in the South Atlantic
  Ocean, annotated as “No FIR.” Flight Information Services (FIS) also
  do not exist in the high altitude structure in other large areas
  (above the top of controlled airspace). Within no man’s land, aircraft
  separation (prevention of collision) is entirely the responsibility of
  the PIC. Advice and information for the safe and efficient conduct of
  flights is not provided from an ATS unit. An ATS unit does not provide
  alerting services related to search and rescue.

Source: FAA 8900.1 - Flight Standards Information Management System - FSIMS (Vol 4-105-C-3)


text:
Is In-Seat Rest used regularly where it is legal, and is it restricted by airline SOPs?
This answer says that a pilot who is not flying (PNF) can make use of a procedure called In-Seat Rest to take a nap during flight.
A comment on the same answer says that this is illegal in the US, but allowed in the EU. Is that true? Where else is it allowed and not allowed?
Is this procedure used regularly in the EU (and other places where it is legal)? Do airline SOPs restrict it?

It is also allowed in Canada. Most airline SOPs encourage it because it is cheaper than adding extra pilots to allow for proper rest breaks.

There is a complicated list of factors relating to maximum duty time and minimum crew rest. In seat rest does not substitute for rest in a bunk.

@MaxPower if you can summarise the factors and turn your comment into an answer, I'll be happy to accept it!

Too complex for me to give a specific answer, and this answer is assuming only airline transport not private flights or business charters.
Duty time limits are different for every country and may involve several pages of tables and definitions, airlines hire people just to track and comply with this.

Time of day relative to the pilots home timezone. If they are working when they are accustomed to sleeping then allowable hours are reduced.
The number of pilots on duty and length of single flight. A flight with 4 pilots is allowed longer shifts than 3 pilots, and a single pilot aircraft will restrict flight time per week more than 2 pilot aircraft.
Total hours worked per week.
Time between rest breaks, length of rest breaks, and location of rest breaks (eg at duty station, break area but expecting quick response(awake), break area without quick response(sleep in bunk)
Shift length, generally the whole period between breaks of 8 or more hours on the ground.(8 hours will vary with jurisdiction, ie some are 7 hours or 10 hours) For example if starting work after holiday: work 8 hours, off for 6 hours, work 7 hours, off for 10 hours. In many jurisdictions this would legally be considered a single shift of 21 hours with a 6 hour meal break.
Days between full 24hour rest days or number of 24hour rest days per month.

Good summary, but duty time limitations have nothing to do with in-seat rest.

Now that would depend on the regulations in your jurisdiction. Would it not?


text:
PZL M28 Skytruck exhaust alignment
Watching a short documentary on PZL M28 Skytruck, I noticed it has quite oddly aligned exhaust pipes.
They point almost directly downwards, with only slight aft tilt:

Picture credit: Łukasz Golowanow & Maciek Hypś, Konflikty.pl
Does anyone have factual information as to why the exhaust is directed such?
Common sense would suggest it is done to keep hot exhaust from hitting the flaps and the wing strut. But when considering the common usage of M28 from unpaved  runways, such exhaust alignment seems odd as it most certainly will kick up all kinds of debris.

I think the flow of exhaust is not significant enough to kick up any debris. It's more likely to avoid blasting the strut with heat and paint discolouration from the exhaust residue. I don't have any facts to back this up so I will refrain from answering.

I stepped into the same trap at first @MichaelHall , after the documentary I browsed the web, not yet knowing M28 is a develpoment of An-28. An-28 has the exhaust at the back of the nacelle, so this must be what you had in mind. M28 uses PT6A engines, hence the different exhaust arrangement.

It looks like there is a deicing cuff of some sort on the leading edge of the wing; it may be that the exhaust is angled down to avoid frying the cuff.

There would be no point deicing such a small area. I think it may be a cuff to protect the strut from hot exhaust.


text:
Can free fall velocity be used to start a ramjet?
A comment to this question suggested, followed by a smiley, that dropping it [a ramjet engine] from orbit might start it. This got me thinking if this really would be possible.
This Skybrary article suggests that the minimum theoretical starting speed for a ramjet engine is as low as about 100 knots, but the same article, and Wikipedia and many other sources state no significant thrust is produced below mach 0.5 (or even higher).
A streamlined object such as a bullet in freefall will reach a terminal velocity of about 90m/s or 175kts, which would be within the suggested theoretical starting speed.
But this is where my math skills fail me: In order to start, the ramjet will need to be able to force air through itself, this will obviously create resistance. Therefore a ramjet might not be described as a streamlined object, and it might not be able to achieve the speed necessary to start and produce enough thrust to further accelerate to an operational speed range.
Further complicating things migh/will be the altitude from which the ramjet migh be dropped. We know that re-entry from orbit will yield vey high velocities, but these are achieved in very thin atmosphere, and I have no idea how this plays with the operation of a ramjet...
So: is it possible to start a ramjet by dropping it from an altitude, and what might the order of magnitude of this altitude be?

A bullet is small. Now scale it up to the size of a truck and see it fall at supersonic speed. Scaling laws are your friend here.

My math fails me on so many levels here

At operating speed, what is the thrust to weight ratio of the vehicle in question? If it is less than 1, then the vehicle can be started by being dropped, no questions asked. If it is greater than one, then math starts to be involved.

This is your captain speaking.  Our engines have stalled, so we're going to go into a rapid descent in order to try to restart them.  Please return to your seat and fasten your seat belts.

A well streamlined body with high enough sectional density can easily fall fast enough to reach ignition speed for a suitable ramjet design (some of the heavier gravity bombs of the Second World War had terminal velocity close to Mach 1, and they weren't optimized to minimize transonic drag).
That said, a very heavy object won't do much flying even once you have thrust and a transonic or faster speed.  The trick here, then, is to drop from high enough.  From sufficient altitude, a falling human in a space suit can exceed the local speed of sound; a streamlined metal object (say, ramjet with fuel tank integrated into duct and diffuser, and some fins for steering, plus batteries and electrics for guidance) should easily be able to carry that kind of speed into thick enough air to support combustion in the ramjet.
As for "how high?" we can reasonably presume that you'll need to be high enough that terminal velocity of a relatively low density object (i.e. one light enough to actually fly once your engine is lit) can get fast enough in thick enough air for combustion.  For the latter, you need to be below about 25 km, so I'd guess you need to be above around 30 km ASL to gain enough speed before getting that far down.  Getting such a device up to an altitude of multiple tens of kilometers is left as an exercise...

There most certainly would not be any sense in this exercise

There most certainly would not be any sense in this exercise Science fiction authors will find some sense in it.  :-)

In fact, you'd launch something like this the same way you launch a Baumgartner: from a stratoballoon.  All you need is higher sectional density and/or lower drag than a human in a pressure suit (both very easy to do), and you can light your ramjet at Mach 1+ and still be around 25 km.

"... is left as an exercise..." often invokes a wry smile.

The inlet of the engine is indeed a source of drag, but it can be covered by some aerodynamic louver until the aircraft picks enough speed. B-36 had the deployable louvers over jet engines to reduce the drag when not running, while these were not ramjets.

Yes, that helps, but isn't strictly necessary. The ramjet-carrying object must be large and the altitude must be high, then starting the ramjet is straightforward.


text:
Can I apply for a Gold Seal any time, or only when I renew my CFI certificate?
Basically my CFI certificate expires almost a year from now, but I have met the requirements for Gold Seal. Can I obtain my Gold Seal now, or do I have to wait until its time to renew my CFI?

I think you can apply at any time, you will be issued a new certificate with the gold seal upon demonstrating your accomplishment to an examiner.

You can apply now. It will be reissued every time you renew your certificate.
http://www.pilotratings.com/goldseal.html


text:
Why are some jet trails longer and some shorter?
One can see  jet trails behind an airplane. I know that they form because of rapid condensation of Jet exhaust. But I can't figure out why some remain for too long time (hence, longer) while  some are smaller and disappear rapidly.  Does this depend on height of airplane or some other parameter ?

Hey thanks, for the answer. Can you tell me, how can I delete my question now?

@AbhishekVerma We prefer if duplicate questions remain, it helps broaden the surface area that searches will reach and helps point people to the correct answer.


text:
What is the purpose of a USB port in the cockpit?
I'm definitely new to the site so apologies if this question is naive but google turned up no answers for me:
I was reading this article and read the following paragraph:

As an example, Hypponen said he had recently spoken to a European aircraft maker that said it cleans the cockpits of its planes every week of malware designed for Android phones. The malware spread to the planes only because factory employees were charging their phones with the USB port in the cockpit.

The question that immediately sprung to my mind was:

What is the intended purpose of USB port(s) in the plane cockpit?

Was it really intended for charging devices like phones? That seems naively insecure.

Welcome to the site! Good question, it was actually just discussed in our chat room.

The fact that it allows them to link to the flight computers is unsettling, but yeah, pilots may have an EFB they want to keep running or something else electronic that needs power, but I don't see why they don't just install a "power-only" USB socket.

Related: http://aviation.stackexchange.com/questions/17621/how-are-avionics-updates-delivered

A USB port that only delivers power (i.e. only for charging) is not a security threat. So, evidently, the USB port is actually connected to the on board systems.

I would treat that article with a great deal of caution.  This quote - Because the plane runs a different operating system, nothing would befall it. But it would pass the virus on to other devices that plugged into the charger is technical nonsense.  Officers of anti-virus software vendors are not to be trusted when talking about viruses.  There are several other quotes which suggest either "bending of the truth" or a lack of understanding.

@MortensenAviation Who said they could connect to the flight computers?

@Simon "Some Flight Management System databases are updated via USB stick and require a USB port."  It is the first line in what is the only current answer to the question posted by Dave.

@Simon: "it cleans the cockpits of its planes every week of malware" means something with computing power has been altered. But I agree that there are many essential elements not provided, as: How is this cleaning done? which would help understanding the aircraft OS (if any). And to answer the question: Indeed the USB port is not for charging devices, else the two data pins would be left unconnected, only the two power pins would be connected to a 5V charger.

@mins I mean, it is impossible for one operating system to pass a virus to another without executing code.  I could go into a long explanation about why this is technical nonsense but it would be wildly off-topic.  SuperUser.SE would be a good place to post a question about this but suffice to say, passing viruses in this manner is nonsense and I simply don't believe the entire "cleaning the cockpit" bit. Any developer who would put a driver behind the USB port, that would execute code from a consumer operating system is too stupid to get through the first interview.

@Simon: I see what you mean, but actually it is possible using DMA and other techniques. The (really) pervasive buffer overflow attack generally doesn't use code, at least not explicitly. Code is ran without asking for, because it's part of the protocol. If you want to post a question on SU, I'll provide an answer.

@mins Yes, but a DMA attack requires the same OS on both sides since the driver must execute code in order to access the address space, although I suppose a theoretical exploit is possible, it would need to be engineered to understand both OSes.  I seriously doubt that any Android malware is targeted at the proprietary OSes installed in cockpit systems.  Just imagine the complexity of trying to transfer a virus from one consumer OS to another.  Once again, the stupidity of a developer who enabled a kernel DMA driver would lead to instant dismissal after the design review.

@MortensenAviation Yes, I know.  My point is that there is no evidence anywhere in the links that this was/is the case.  The whole story has more holes than a good Swiss cheese.

@Simon: DMA: The initial demo was to read a PC from an iPod, the target OS is actually not involved (DMA and Fireware are features of the motherboard). For the question here, I'm not either convinced of the "virus" story, as it is reported. I can't continue on this thread here... this is really off topic.

Some Flight Management System databases are updated via USB stick and require a USB port. Since navigational databases are updated frequently and require a simple way to make an update, USB (or memory card slots) are generally used to allow for rapid and easy updates without having to remove any panels. In some cases the port may be in the avionics bay however that is usually easily accessed as well. It should be noted that a recent change in regulation now allows pilots to update nav data, this question covers it well.

Was it really intended for charging devices like phones? That seems
  naively insecure.

Generally these ports are not for charging but the basic design of a USB port more or less always allows you to charge from it because of the nature of the port. The security on the ports is more about cockpit security. In most cases the security lies in making it difficult to get into the cockpit in the first place. It is often assumed now that if you are in the cockpit you should be there. There is of course many questions this opens up some of which have been answered here or would be good to ask about.
As iPads become more common in the cockpit for navigation and the such USB ports are becoming more commonplace on panels for charging but this seems to be more common in GA planes currently.

But why would the USB port for software updates be in the cockpit?  Seems like a better (or at least more secure) design would be to have it behind a panel somewhere, with the rest of the avionics.

See my edits above.

Thanks for the concise answer and links included. Good point that if you're in the cockpit you could always just crash the plane anyways, so being able to inject malware is petty in comparison, but the fact that the pilot/copilot could unintentionally be allowing hijackers into the software running the controls is still a bit scary (assuming the article is to be believed)


text:
How does the VOR receiver pick up the signal and how are the needles controlled?
Knowing the basic principle of a VOR and how it works, I am interested to know how the receiver works.
What exactly makes the needle deflect? And how does this deflecting mechanism know how much to deflect the needle?
So here is what I am thinking so far: since the signals are sine waves (I guess) and there are two of them, if you lay them over each other there should be a unique voltage for every direction from the VOR. To keep on guessing, this voltage is probably amplified and put onto a electric magnet that will then control the needle's deflection.

This might be better in Electronics.  I don't know any pilots who know the internals  of VOR receivers.

@rbp: Does it say anywhere that this site is for pilots only?

Your basic understanding of the underlying electronic principles is correct: The VOR receiver detects a phase offset between two signals, which tells the receiver what radial the aircraft is currently on. Wikipedia has a decent explanation, and this article on Digital Flight Instructor has a nice widget you can play with to see the frequency offset.

The underlying electronic principles the receiver uses are generally not useful for pilots: if your VOR receiver dies you're not going to hook up an amplifier to an oscilloscope and try to sort out the phase offset yourself, if for no other reason than your head would be buried in the cockpit staring at the oscilloscope as opposed to looking out the window for traffic or watching your flight instruments.
  In addition, the "strobe and sweep" explanation is generally easier for students to understand: Imagine the VOR station has two lights, a white light that rotates, and a red strobe that fires ever time the white light passes the 0 degree (North) radial. By counting the time between when you see the red strobe and when the white light passes you its possible to determine what radial you're on.

The mechanism by which the needle is deflected depends on the type of indicator, but it basically boils down to "The receiver does some magic and converts it into a number of dots of deflection on the indicator". The deflection can displayed by moving needle attached to a meter (applying a specific positive or negative voltage), blinking some LEDs, or showing a graphical representation of the CDI (e.g. on a GPS display) with a mark over the appropriate dot.
How this works for each specific indicator is generally only of interest to an avionics technician, and the information would be contained in the service manual for the radio and indicator.

Yeah I know it is kind of useless knowledge, but I'd be really interested in it ;)

Is this forum only for pilots?

@rbp even if the site were "only for pilots" I'm of the opinion that pilots should have some fundamental understanding of how the equipment in their aircraft works: We don't let people get out of flight training thinking of the engine as a magical noise-making go-machine, but most flight schools (and pilots) are content to think of nav systems as magical black boxes. Knowing how the VOR receiver does its magic probably won't save anyone's life, but it's still not a bad thing to know.

I was only riffing on Hennings comment to me

@rbp I know, I'm just one of those "crusty old guys" - I still make junior sysadmins learn vi and expect drivers to be able to change a flat tire without calling the auto club.

Here is a great example of why flight crews need some understanding of the electronics.  In this case, the ILS reported it was working properly, when it was not.  The flight crew knew this was possible, and had a basic understanding of why.

"The receiver does some magic" What kind of magic does it do?

@usernumber to answer that I would need two additional pieces of information: The type of receiver/indicator being used, and the service manuals for them. (It depends on what type of receiver/display is being used: The digital CDI on a GPS display is driven differently than the analog meter-movement unit attached to an old KX-170)


text:
Is there any limit by FAA on the age of aircraft to be operational?
Is there any restriction by FAA that one can not fly a plane older than 'X' years?
If someone is maintaining an older plane (e.g. from 1990s), are there any regulations which prevents or restricts that person to fly that airplane?
I am interested in finding out both for commercial and smaller general aviation airplanes.

I don't have anything particularly constructive to add, but I just thought it was funny that you mentioned someone "maintaining an older plane (e.g. from the 1990s)"  As General Aviation planes go, that would be a practically brand new plane.  heh

hahaha at '90's being old. The plane I learned to fly on was "built" before I was. And I aint that young!

I sometimes fly a glider built when my grandfather was a toddler...

It depends on the aircraft, but in general the answer is that there  are no regulatory age limitations, and indeed we have many aircraft flying that are 50+ years old.
A notable exception is the Robinson line of piston helicopters. The airframe on those helis is limited to 2200 hours or 12 years, whichever comes first, at which point the entire airframe must be completely overhauled. Some of the airframes are indeed rebuilt, but some are also scrapped, depending on level of wear and corrosion.
Since the airframe lifetime is in the LIMITATIONS section of the POH, it is governed by:

§ 91.9 Civil aircraft flight manual, marking, and placard
  requirements. (a) Except as provided in paragraph (d) of this section,
  no person may operate a civil aircraft without complying with the
  operating limitations specified in the approved Airplane or Rotorcraft
  Flight Manual, markings, and placards, or as otherwise prescribed by
  the certificating authority of the country of registry.

It's worth noting that the limitation on Robinson helicopters is a manufacturer limitation, not an FAA one. (It has regulatory authority because of where the manufacturer elected to put it in the manual, but if Robinson had published that as a Service Bulletin instead of an airframe Limitation many operators wouldn't be bound by the requirement).

You could say that about any limitation, like an aircraft capable of IMC but not certified for IFR

Well I can say it about every limitation I'm familiar with: All the ones I know of are manufacturer-imposed (per the maintenance manual or AFM/POH Limitations section). The FAA does have the regulatory authority to life-limit components or airframes (and to impose other limitations) through ADs if they feel it's necessary and the manufacturer doesn't have a stated limit, but I'm not aware of any case where they've actually done that.

Here's an example of life-limiting a glider via AD (section on wing spar fatigue) http://en.m.wikipedia.org/wiki/LET_L-13_Blan%C3%ADk

Leave it to Australia to be a viable example :-) (It seems the FAA simply grounded the fleet?)

N60094, a 1909 Bleriot XI based at Rhinebeck Aerodrome Museum, has a valid FAA airworthiness certificate.  So I think it's safe to assume there are no FAA restrictions based solely on age.
]1

Let me pick a nit. There are many non-certified aircraft flying in the experimental category or under an LLOA, so one example doesn't answer the question in general.

One case of no lifetime limitations does not disprove the existence of lifetime limitations.

@casey: But one case of no lifetime limitation does disprove existence of blanket lifetime limitation. Which was after all what the OP was asking for.

Your link to the FAA is the registration, not an airworthiness certificate

Aircraft hulls are limited in the wear and tear they can withstand due to metal fatigue that can develop (pressurized aircraft more than non-pressurized).
The manufacturer will impose limits on the flight time of the hull (an older airframe will be considered not airworthy) so any developing metal fatigue will not tear apart the plane in flight like what happened with the Comet or Aloha Airlines flight 243.
tl;dr it's the responsibility of the manufacturer to impose limits on the airframe age.

The limit is not flight time, but always flight cycles.

@JanHudec expressed in flight hours usually, it's that aloha flight that made it clear the amount of cycles is the more important factor

And this doesn't answer the question of regulatory age. Any airframe, regardless of age, that is not airworthy is, well not airworthy

@JanHudec The limit is not always expressed in flight cycles, though that's often what they're trying to capture in an "hours" limit. For pressurized aircraft I've never seen one that doesn't list a cycle limit, but non-pressurized aircraft often have service limits expressed in hours (flight time) without a corresponding cycles limit. The wing life limits on Grumman's AA1 & AA5, Piper's Tomahawk, and the Cirrus SR20 & SR22 all fit that description.

@voretaq7: True; I had pressurized aircraft in mind.

According to Wikipedia the DC-3  first flew in 1935, entered regular passenger service in 1936, and as of 2012 #10 off the production line was still in regular commercial service. I'd venture to say it's got more to do with maintenance than regulation. (I'm sure someone will quote the appropriate FAR section in a few minutes.)

The DC-3 doesn't have a pressurized cabin, though, right?

With a service ceiling of 23,200 ft, I don't think it does.

Yeah, so its airframe wouldn't have to deal with the continual pressurize/depressurize cycles that a modern airliner has to deal with. This is part of why you still see such old piston engine aircraft still in service, but you don't see that with jet airliners.

@reirab: Maybe older jets just aren't airworthy or cost-effective to maintain. There may not be any more Comets in service, but there are 707s still flying freight or charter service. And the USAF still flies KC-135s and B-52s, and those airframes are from the 1950s or 60s.

@Gabe 707s were built all the way up to 1979, though. The KC-135s didn't even start delivery until 1981 with production going through 1987. Also, military airframes don't get as many cycles (or as many flight hours) as airliners, so that's also part of the reason for longer service life there.

@reirab The real difference between GA/airliner is in the hours of operation per year.  Typical GA aircraft has MUCH less use per year, so pressurized or not, there's less wear and tear on the structure (although it continues to be exposed to corrosion).  A general rule of thumb for GA aircraft is when you get around 10,000 hours on the airframe it's time to replace/major overhaul even if no corrosion is found in routine inspections.

@reirab No, you're thinking of the KC-10. The KC-135's production started in 1955, its first flight was in 1956, it was introduced into service in 1957, and its production ended in 1965 (none are newer than that). It actually predates the 707 (it's not based on the 707, both are based on the 367-80).

@reirab: You're definitely right that mission profiles differ significantly between civilian and military planes. I don't know if any of the current inventory were involved, but B-52s once had extremely stressful training missions and Operation Chrome Dome had them on continuous patrol for some 8 years. Also, KC-135s were delivered from 1957 to 1965.

@cpast You're right. My bad. I looked at the KC-135 first and got sidetracked looking at the KC-10 and forgot I still had its page up when I grabbed the number. - haha

A down vote? After 16 months? Care to explain why?

DC-3s have no structural life limits but there is a mandate to remove and inspect the wings at 10,000 hrs time in service.
Just to clarify, an aircraft is not "certified". The proper term used by the FAA is,"certificated"- meaning each aircraft model has been certified and a specific Type Certificate has been issued.

As a general statement aircraft are pretty well-built (in fact, they are generally overbuilt so they'll hold up to use and abuse in excess of their stated design tolerances), and carefully maintained. As such there is generally no regulatory restriction on airframe age, though there may be other applicable restrictions (or recommendations) depending on the aircraft.
The most common restriction you'll encounter that's similar to what you're asking about is what are known as "life-limited parts" - Aircraft components that have a finite limit (expressed in flight hours, flight cycles, or calendar time), after which they must be replaced or overhauled.
These limitations are usually given by the manufacturer (in a Limitations section of the POH/AFM or Maintenance Manual, which has regulatory effect under FAA rules).
In some cases an entire airframe may be life-limited: (The R22 helicopter has both a calendar and hours limit,  and commercial airliners typically have a flight cycle and flight hour limitation on the airframe as well.
In other cases only a component may be life-limited: The wings on a Grumman Tiger or a Piper Tomahawk must be replaced after a certain number of flight hours.

Even in absence of a specific limitation it's important to recognize that all airframes have a finite life - components will eventually suffer fatigue and fail, as with any kind of mechanical equipment. Manufacturers may recommend extensive inspections of older aircraft to ensure that fatigue is detected before the structure fails. (For example, while the Piper Cherokee family has no Limitations published Piper does recommend extensive inspections on aircraft that have accumulated a large amount of flight time.)

Another example for your list: the wings/wing spars on the piper seminole PA-44-180 and -180T are life limited to 14,663 hours (per the type certificate). http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/21318cbc7610d2f786257d81005a094d/$FILE/A19SO_Rev_14.pdf

@casey Yup, that's another good example. There are also sometimes components that are limited by AD (AD 95-26-13 on oil cooler hoses, and in Australia flight control cables need to be replaced after 15 years.)


text:
How do passengers board the planes on this airport?
I found a quite "rare" layout on Munich airport. It has jetbridges but I don't see any terminal. Look:

How do passengers make it to this point of the airport? By underground?

Either this is an optical phenomenon caused by stitching satellite images together, or they get to the jet bridges by way of a bus (which you can see in the image), it looks to be the latter of the two options though.

That's where they park the bad planes. Fine. I don't like it, but you can land here. You're parking in the boonies, though...:.

@mins The bus gates are in T2 but these stands are in T1 side. The apron jet bridges are used by both terminal and the bus gates are used for planes in apron with/without jet bridges.

They are specially designed apron jet bridges. It looks like the normal gates but required to transfer passenger by bus.
A model shows how it runs (credit) :

LAX has a number of apron jet bridges just south of rwy 6R. Their advantages over typical airstairs include having escalators to raise the pax rather then depending on stair-climbing and they keep people out of the weather. Note the overhang along the roadway for the buses to park under. It's been a few years now, but often having used the LAX apron jet bridges versus airstairs at, say, Tel Aviv, I remember the apron jet bridges as being significantly faster. And watching and waiting for old Hajjjis having to contend with airstairs at Jakarta during five hajjes was truly painful

I want to fly such a colourful plane!

@kepler22b: Except sooner or later you're sure to get an idiot who wants to look inside a jet engine :-)

This type of terminals are called "Satellite Terminals". Passengers are usually processed in a central building while aircraft are parked in remote docks. The satellite buildings are connected with the central building (if any) through tunnels or any kind or collective transportation (e.g. bus).
These terminals have a wide range of advantages and disadvantages when compared with more frequent types of terminals.
Advantages:

Suitable for high traffic airports and hubs with a large number of connecting flights.
Easiness for the aircraft to maneuver on ground.
Easy separation of passengers flows (e.g. international pax, national pax, regional pax).

Disadvantages:

High investment and maintenance of transportation services.
Acces congestion at peak-times.
Early check-in.

Munich (MUC) or Madrid (MAD) are some of the airports that have implemented this system.
The photo you show seems like a very special kind of satellite terminal with multiple remote "gates" and are probably managed by a bus that travels through the road connecting all of them.


text:
Are there examples (current or historical) of commercial aircraft seating arrangments beyond the standard today?
Excluding various first-class seating arrangements, are there any examples in history or today, of an airline that has implemented a non-standard seating arrangement?
For instance, most military transport aircraft contain just rows with passengers' shoulders inline with the bow and aft. Are there any examples of where a commercial airline has tried this arrangement -or any other type?
An extreme example would be an airline like a subway car (everyone standing up, just hanging on to something).

Subways are used to travel shorter distances, and they go at a much slower speed. Airplanes can be compared with intercity trains for a closer comparison in seating configuration.

That subway car position could happen on Soviet airliners - passengers sometimes got up during descent and were standing in the aisle during landing, so they could leave the aircraft sooner.

Some of the old flying boats had a seemingly haphazard arrangement

Source

Source

Source
But maybe all flying boat passengers were effectively first class?

Great collection of pictures! Reminds me of the seating on Zeppelins, especially the last one.

yes, you're showing the first class cabins. Flying boats (at least the big ones) were used effectively like passenger liners. Day cabin, dining room, and passenger cabins with bunks (or seating arrangements like in the picture you show, probably a shorter range one).

The pictures are great, but yes, these are essentially 1st class (well, they put first class to shame really).

Current FAA passenger safety regulations require seats with 16G survivability:
http://www.faa.gov/passengers/fly_safe/safety_improvements/media/FAA-FactSheet-Aircraft-Survivability.pdf
As the PDF notes:

In 1988, the FAA issued regulations
  requiring that all newly developed
  transport aircraft use “16g” seats.
  Using a test dummy, these seats
  undergo dynamic testing and
  evaluation regarding injury
  protection. Similar to automobile
  crash tests, the FAA tests are
  designed specifically for the aviation
  environment. Previously, seats were
  designed and approved to a static
  9g standard with no occupant
  injury criteria. Most transport
  airplanes were developed before
  1988. However, Amendment
  121-315, effective October 27,
  2005, required that transport
  category airplanes in part 121
  operations, certificated after
  January 1, 1958 and manufactured
  on or after October 27, 2009, must
  comply with the 16g dynamic
  standard. In 2010, the agency
  published guidance on the
  importance of analyzing how interior
  structures, such as seats, interact
  with other structures due to critical
  loads. In July 2012, the FAA issued
  new criteria for side-facing seats
  that are equivalent to the occupant
  protection for standard
  forward-facing seats

It is very hard to design side-facing seats that meet these survivability standards (human necks are very weak in the lateral direction). Furthermore, the airplanes are current designed with seats that slide on tracks in order to make the cabins easily customizable to customer (airplane company) requirements. This also makes it easier to design around front-facing seats:

And let us not forget this quickly abandoned proposal. Everyone would still be facing forward but we'd be standing! With shoulder and waist harnesses (five point), survivability might actually be pretty good! Actually, I'd want a head and neck retainer too. :-)

Not sure if those are excluded by the "Excluding various first-class seating arrangements" part of your question, but there are a few slightly more original layouts that have been used (or are still used) by some airlines, mostly for business class:

the herringbone pattern. Seats are arranged at about 45° from the axis, and all seats get direct access to the aisle.
reversed seating, as for instance in British Airways' Club World (business class): in a given row, alternating rear- and forward-facing seats. This saves a bit of space laterally (you need more space at the elbow level than for the legs, so by having one person's elbows be at the level of another's legs, you can have more seats in the same width).


text:
When will Europe allow phones (to communicate) on planes?
Currently USA has allowed phones to be used in commercial flights, is there a similar ruling coming to Europe or will my mid air Bluetooth battles have to wait?

AFAIK, there has already been talks made by 1/2 big operators to allow phone and should be in by the end of 2015

What do you mean by "to communicate"? If this is using the wi-fi or bluetooth, you can as long as the aircraft is equipped with wi-fi or as long as you operate your own wi-fi access point. To use cellular connection you need the aircraft to be equipped and the airliner to have a aggrement with a cell phone company. The cellular network is not designed to connect phones that are at high height (more than few tenth of meters).

There is a similar ruling since last week.
The use of electronic equipment as long as they are in "flight mode" during all phases of flight was already allowed in Europe by EASA since November 2013.
Since last week (26 November 2014) EASA also allows phones to be on and connected throughout the flight. This allows for WiFi services, phone services and Bluetooth battles during the flight.
Before allowing the use of these electronics in flight, airlines have to assess the impact of the signals transmitted by the mobile devices on the aircraft, ensuring aircraft systems are not affected. For this reason mobile communication will not be allowed by all airlines on all flights at once.


text:
How many active large commercial airplanes are there?
For example, the 747 Wikipedia page says that 1500 747s were produced (that number seems quite low!).
Any indication of how many large, commercial aircraft there are, and what the breakdown between passenger and cargo is?

This is a hard question. The definition of active and large should be precised. You can easily find the number of sold aircraft, but the number of aircraft that has been decommisionned is not obvious.

After defining large and active you could try to use the historical data at flightradar24.com to actually count this number instead of doing an estimate.

As mentioned this question is hard to answer very accurately without better access to data. It also depends on your definition of "large, commercial aircraft." Including all wide-body aircraft would be a large number of planes, and the totals are constantly changing as aircraft are delivered and retired.
This site will probably be the best resource for this kind of question. The data is probably not 100% accurate but it seems to be close. Other information is also available here.
I looked at the widebody models on the first linked site, sorting by status to find how many are in "Active" service. This does not include "Stored" aircraft which will be either put into service or not.
The models below total: 1026 cargo, 3825 passenger. This means about 21% of the 4851 widebodies are cargo aircraft, and widebodies constitute about 24% of the worldwide commercial aircraft fleet of 20000 aircraft.
747
There are 652 aircraft in service of 1500 delivered to date. Of these, about 289 are cargo aircraft. Excluding 28 aircraft operated by militaries or other organizations, this leaves about 335 passenger aircraft.
DC-10
There are 69 aircraft in service of 446 delivered. This does not include aircraft in military or firefighting services, or the aircraft used by Orbis.
A300
There are 255 active of 561 delivered. Excluding 6 in military or other service, this leaves 178 in cargo service and 71 in passenger service.
767
There are about 821 767 aircraft in service of 1062 delivered. About 165 are cargo versions, and excluding 16 in military or other service, this leaves 640 in passenger service.
A310
There are 105 active of 255 delivered. Excluding 17 in military or other service, this leaves 14 in cargo service and 74 in passenger service.
MD-11
There are 153 aircraft in service of 200 delivered. Only 3 of these are passenger aircraft. These are operated by KLM, and the last scheduled flight is October 25, 2014.
A330
There are 1069 active of 1112 delivered. Excluding 22 in military or other service, this leaves 27 in cargo service and 1020 in passenger service.
A340
There are 289 active of 377 delivered. Excluding 11 in military or other service, this leaves 278 aircraft in passenger service. If there are any versions used only for cargo, there aren't many.
777
There are about 1216 777 aircraft in service of 1230 delivered. About 134 are cargo versions, leaving about 1082 in passenger service.
A380
There are 139 delivered. There are no cargo variants and none out of service.
787
There are 183 delivered. There are no cargo variants and none out of service.

There are several ways to estimate the answer. One would look at the number of delivered airplanes per year, and the other would start from the total number of passengers per year. See here for data for both methods.
Airbus and Boeing together deliver almost 1000 airplanes per year. If we set a lower limit of 150 seats for what counts as a large commercial aircraft, 1000 planes would already be a good estimate for global production. If we now assume that an individual aircraft will fly for 30 years and factor in the growth in delivered airplanes per year, the worldwide fleet would be around 12.000 aircraft. There are a few airplanes which start their life as cargo aircraft, but most are converted from old passenger aircraft. For now, I would assume that all newly built aircraft will go into passenger service.
How many airplanes would be needed to ferry 3 billion people per year? Short-range aircraft can fly 5 times a day when well managed, and long-range aircraft still manage more than one flight per day. Since the majority of flights is short range, the average number of flights could be 4, with 230 seats and 75% load factor on average. This comes out to 3.000.000.000 / 4 / 172.5 / 365 = 11.912 planes.
Looks like 12.000 is a reasonable estimate for the worldwide total of large commercial passenger aircraft.
Using ICAOS number of 16 billion freight ton-kilometers of air cargo volume worldwide, and guessing an average load of 30 tons over 2000 km, it would need 266.667 flights to ferry this volume. If a freighter flies twice a day, the total number of freighters could be just 365 aircraft. This would be just 3% of the number of passenger aircraft.

Edit:
The first estimate leaves out all aircraft smaller than 150 seats, which should be included in the ferrying of those 3 billion passengers. I think my utilization estimate is too high; a better number would be 2 flights per day. This moves the total number of commercial passenger aircraft to 24.000, but includes small ones which a correct answer to your question should not include.
So my money is still on 12.000 for aircraft bigger than 150 seats.
Also, cargo aircraft should be more numerous; again my utilization is on the high side, I guess. But I would be surprised if there are more than maybe 800 big cargo jets in operation worldwide.

@fooot: I agree, and I guess my flights per day are on the high side. But the answer should show how to approach the question in general. And would you count all the aircraft in storage? The boundary of the question is not well defined.


text:
Which FAR/AIM addresses Shortest Turn to Assigned Heading vs Runway Traffic Pattern?
Today I was in a simulator on runway 20R at KSNA. ATC gave me a VFR clearance and told me to fly heading 080 on departure. The runway has right traffic. I turned right and was told by ATC I should have turned left because you're supposed to always take the shortest turn to assigned heading when given a heading, even if the runway has an opposite traffic pattern.
My question is: Where does the FAR/AIM specify this rule? Are there any other legal publications that specify this?
Bonus points if you can cite a reference to this rule in any PPL textbook e.g. Jeppesen's Guided Flight Discovery Private Pilot. Thanks.

Did they give you a turn direction, e.g. "turn left heading 080"?

No. I think that may have been part of the test because I think in the real world they would say 'left turn approved' or something like that. So the question is: When they leave it unclera, what should you do? Left turn or right turn?

Actually, in the real world, you'll probably just get a heading in your departure clearance. If you don't get a heading, you need to fly runway heading. There are a lot of technicalities when it comes to flying IFR, and a lot of the rules are not obviously in the regs. Then again, you were VFR, so I'm not sure what's up with that.

The most important point is that if any ATC instruction isn't clear then you should just ask them to repeat or clarify it.
Having said that, turning in the shorter direction is stated in the FAA's Pilot/Controller Glossary:

FLY HEADING (DEGREES)- Informs the pilot of the heading he/she should
  fly. The pilot may have to turn to, or continue on, a specific compass
  direction in order to comply with the instructions. The pilot is
  expected to turn in the shorter direction to the heading unless
  otherwise instructed by ATC.

In my personal experience, ATC almost always say left or right for heading changes if you're on an approach or departure, but sometimes leave it out if you're in cruise. That makes sense to me: the busier the airspace the more they want to make sure that you don't turn the wrong way.

Thanks! Yes I think the point here is that unless you know this regulation, there is no uncertainty on whether it's clear or not, you'll simply fly the runway pattern and so won't ask for clarification.

It's also important to note that @seattle272SP's example isn't actually a heading change, it's an initial departure heading. Those are a different animal.


text:
What is Cost Index?
I'm not sure if it's just in Boeing aircraft, but I've heard that Cost Index has something to do with flight planning but have no idea what it is.
What is it for and how is it calculated? (I'm happy for the simple version of the calculation if it's too hard to explain)

The cost index is a number used in the Flight Management System (FMS) to optimize the aircraft's speed. It gives the ratio between the unit cost of time and the unit cost of fuel.
With this number, and knowledge about the aircraft's performance, it is possible to calculate the optimal speed for the aircraft, which results in the lowest total cost.
Speeds slower than the optimal speed will result in less fuel burn, but also in more flying time. The cost of the extra flying time outweighs the fuel savings at speeds below the optimum speed.
Speeds faster than the optimal speed will result in more fuel burn, but also in less flying time. The saving of less flight time do not outweigh the fuel burn at speeds above the optimum speed.
A low cost index means that the cost of time is low or that fuel is expensive. It will result in a low speed. High cost index means high cost of time (e.g. passengers about to miss their flight connection) or low fuel price (rare these days).
At the minimum cost index (0) only fuel counts. This will result in the aircraft flying at Maximum Range Cruise. At the maximum cost index only time counts. This will result in the aircraft flying at Maximum Cruise Speed (Vmo / Mmo with a buffer)
Airlines generally have a standard cost index they use for planning and adjust them on a flight by flight basis.
This document from Airbus explains the cost index in more detail.

Great, thanks for the information.

According to this article, Cost Index of a flight is:

The ratio of fuel costs to all other costs.

So the lower the Cost Index, the lower the fuel burn in relation to the other operational costs of the trip.
This generally means flying the airplane slower and higher in order to conserve fuel, but that is offset by the higher maintenance costs due to the airplane being in the air longer and inspections becoming due sooner, so is true only to a certain point.
It is a generic term, not specific to Boeing.

While somebody else might be able to explain it better, Cost Index is the relationship between fuel use and flight time.
High Cost Index: Fast flight, low crew times, high fuel use, etc.
Low Cost Index: Slow flights, high crew times, low fuel use, etc.
It's always a complex compromise on what is best, and policies vary between airlines and how they use their aircraft. I don't think you can 'do' a calculation though in that sense, since it's a value which often comes from computer formulas.

Cost Index is the ratio of time related cost to Fuel related cost. The time related cost considered, is the fixed cost.
The time related costs (airplane operated costs affected by flight time), include but:
-flight crew
-cabin crew
-leasing
-maintenance (time related) -airframe material /labor
-engine material /labor
-other costs
The time related costs may be difficult to calculate. You will have to get the time related cost form your account Unit/department
The fuel costs are expressed in units of currency per quantity of fuel :cents/pound, while the time related cost is USD/min


text:
When are multiple hops more efficient than single leg?
Considering a very long route (equal to the max ferry range of an aircraft[1]).
Would it be more fuel efficient to fly multiple legs or a single one ?

Multiple legs would allow you to use less fuel, decreasing weight and fuel consumption
Single leg would dispense you having to go through multiples takeoffs and time increased at low, high drag altitude

How does theses balance ?
I'm interested into any real world aircraft[!].
[1]: Results might differ for each models so you can pick any you like.

Are you asking for airlines, or general aviation, or both? Are you wanting to factor in revenue or just the fuel and costs?

@slookabill Both are equally interesting. I suspect GA planes to lean more on the multiples hops tho, since they usually fly quite low anyway.
I'm mostly interested into the fuel cost, tho a bigger picture is also welcome.

I have seen flights on fr24.com that show some flights that fill up at 2 airports in a relatively short leg before taking a long leg to the destination.

What does efficiency mean in this context? Least time? Least fuel consumption? Most profitable for an airline?

@Antzi: Personally, the reason I (and I suspect many GA pilots) tend to break longer trips into multiple hops has nothing to do with fuel.  It's bathroom breaks.

A good read: When slower was faster

@ZachLipton: Least consumption. A bigger picture is always welcome tho.

related

In real world, you must find airports to stop not far away from the planned route to make your comparation. It may be hard since ETOPS rules allow airliners to fly long distances far away from the nearest airport, e.g. over large parts of ocean.

Just a nitpick: Drag is lower at lower altitude due to the higher Reynolds number, at least when the aircraft flies at the same lift coefficient.

If the total distance is long enough, flying it in several trips is more fuel efficient. In this answer I have used Breguet's equation to calculate the fuel required to fly a fully loaded A320-200 over 2000 km and 5700 km. The first trip needs 5 tons of fuel while the second needs 18.1 tons. This means the longer trip needs 27% more fuel per km of distance because more fuel is transported and the aircraft is heavier over most of the trip.
However, flight through lower, denser air is less efficient in terms of distance flown per unit of fuel burnt, so you need to find an optimum between flying mostly near the ground and flying with a heavier aircraft. On the other hand, the lighter aircraft will climb much faster, so the time spent at low altitude is lower per climb segment in case of the staged legs.
In the end, if the total distance is big enough to allow for several hops while still only a fraction of the total flight time is spent at lower altitude, the overall fuel consumption is easily lower.

In a broad sense, if the flight distance is nearly equal to the max range of the aircraft, the route with shorter legs is prefereable from the point of fuel economy. The reason is simple- more the fuel you carry more the aircraft you have more weight, which requires more fuel.
All other things being equal, the fuel caried is payload- one can see it as the aircraft carrying extra payload or as the fuel eating into the regular payload. Either way, the extra fuel carried impacts on the fuel effeciency of the aircraft negatively.

According to this document, payload burns fuel at the rate of 2.5-5 % of its weight in fuel per flight hour. For the longest non-stop routes in service, the travel time is in the upwards of 15 hours. Taking a value of 3% fuel burn, this means that a significant portion of fuel consumption is actually to carry the fuel itself. This is a significant issue, especially when the oil prices are high.
The increased take off weight will result in more thrust requirement, TO length and time to climb (or more thrust again), adversely affecting the fuel consumption, while increasing engine wear.
While it is true that the longer distance flights spend more time in altitudes with less drag, it is questionable whether that translates into any significant real world benifits. For example, the latest 777 ULR version has a higher aspect ratio to reduce drag, requiring the folding of wings.
Of course, fuel use is only a part of the story. The other significant factor is time- most of the ultra long range flights are targeted towards business flyers, for whom the addition of more than 25% due to shorter legs may be unacceptable. In the end, the deciding factor may be the percentage of seats filled per flight. When SA cancelled the Singapore-Newark flight, one analyst noted:

“The plane burns a lot of fuel but carries very few passengers,” says Siyi Lim, an analyst at OCBC Investment Research in Singapore. “It didn’t make sense to continue.”

The ultra long distance flights also require additional facilities- extra crew for rotaion, extra food items carried etc. In general, the straight long distance routes have higher fares compared to the ones with stops in between.

The answers to this question seem to contradict this. I think your SA example is not really what the OP was asking. Any flight that doesn't have enough passengers to pay for the fuel burn is likely subject to cancellation. I think he's asking with all other variables removed is it more fuel efficient to stop and fill up. Not saying you're wrong, it just seems to conflict with what they're saying on that other answer.

@TomMcW  I don't think it's a contradiction - the other answer is talking at the opposite end of the spectrum (50km flights) whereas this answer applies to the 18 hour trips. I think the Singapore-Newark flight is a good example but the quote alone here doesn't provide enough context. That flight took so much fuel that it could only carry about 100 passengers, so it would require fewer empty seats to become unprofitable compared to regular flights.

I agree with you for GA flights that stay below 10,000 ft. The extra weight of fuel in the early part of the flight is probably more significant than the fuel burn for landing/takeoff sequence. But I'm skeptical about this assessment for bigger aircraft. I ran some numbers through an online flight sim calculator and got a way different result. I'll post it as an answer. Feel free to read it and point out what I missed. I'm open to criticism

@Ben That flight took so much fuel that it could only carry about 100 passengers Not so according to Airbus website. They say the A340-500 that was on the route is "capable of flying 9,000 nautical miles with a maximum passenger payload," of 375 pax. They were originally flying it with a 181-pax, two-class layout. They couldn't fill that so they reconfigured for 100 pax at a higher price. The nonstop failed for supply/ demand reasons. Much easier to fill a 2-leg flight

@TomMcW Ah you're right there, and I now distinctly remember reading an announcement when they got rid of the economy class seats (for the second time, IIRC). Still, such an ultra-long haul flight has tight economics to begin with because as you're so heavy, you do use more fuel on an hourly basis - http://aviation.stackexchange.com/questions/931/how-does-flight-duration-affect-the-hourly-fuel-consumption-in-heavy-aircraft.

For GA aircraft that stay at lower attitudes carrying the extra fuel for a direct flight certainly amounts to more fuel burn. But It seems to me that, in the case of large airliners, the process of landing then taking off would burn more fuel than just flying past. So I ran some numbers through a flight sim fuel calculator to see what I got.
I used the calculator at Simbrief.com. I have no idea of the real-world accuracy of it, but it took a lot of variables into account.
I used a their 777-200ER model for a flight from LAX to JFK with 250 passengers. BOS was alternate. I routed it over the MCI VORTAC (which a great circle route comes within a few NM of anyway).
It calculated trip fuel at 54,878 lbs.
I then ran it with a stop at MCI. I used the same SID out of LAX and the same STAR into JFK.
It calculated the LAX-MCI leg fuel at 32,280 lbs, and the MCI-JFK leg at 28,676 for a total trip of 60,956.
Stopping at MCI took 6,078 lbs. more fuel,which is about 11%.
The farther off the route the stop is the bigger difference that would be. The reason non-stop flights generally cost more than connecting flights obviously has more to do with economics, passenger logistics and convenience than fuel cost.

That's an interesting software, I will have a go myself later on! But your example isn't answering the question -- the OP is asking about a flight equal to the maximum range of the aircraft. LAX-JFK is pretty short for a 777. In your example yes, stopping at MCI would add 11% of total fuel, but if you did LAX-SIN (for example, and assuming that software is realistic), a stop over somewhere in between would add a lot less, and would maybe even save fuel. The reason is because you're burning extra fuel just to carry more fuel, whereas you could do two legs at a lighter weight.

Consider this: I don't know if you are into Formula 1 racing, but drivers can choose to have a pit-stop once, twice, or even three times during a race. It might not make sense to pit more than the bare minimum, right? Well, by pitting more often, they don't carry as much fuel, and therefore are lighter and have quicker lap times. This strategy won't work if the race is only 10 laps long, but if it is long enough you could win the race. It's similar with flying. Figuring out at what point 'long enough' is in order to make the stop beneficial requires airline data and many smart minds.

@Ben That makes sense. I just used LAX-JFK because I happened to know MCI was right in the middle. Took quite a while to crunch the numbers. If I get a chance I'll try a longer route. And, like you said, I have no idea how accurate that site is. It's made for flight sims. I don't have access to any real-world planning software and I couldn't find good reliable numbers to do my own calculation.

One factor I haven't seen mentioned is that many GA pilots like to fly with excessive reserve fuel (far beyond FAA requirements) as a safety margin. In addition some operators keep the tanks full in order to avoid condensation* in aircraft which tend to sit for long periods. For those reasons it is not unusual for a GA flight to carry significantly more fuel than it needs on any given leg. If you're going to carry a full tank anyway, it will certainly be more efficient to make the trip without stopping.
Airlines are obviously critical of waste related to carrying excess fuel and have policies in place intended to ensure that no more than the minimum required fuel is carried on any leg. The closer that works out to being true, the more relevant this question becomes. But knowing my share of airline pilots, I also find that the more disgruntled they are, the less inclined they are to pinch pennies for the boss. i.e. The benefits gained from flying shorter legs will likely be partially negated by carrying excess fuel anyway.
* Regardless of whether the condensation theory has merit, storing the tanks full is commonly taught as good practice.

If the aircraft is stored with tanks full, would that fuel be siphoned out in case the pilot wants to fly a short leg ?

That's an option but highly impractical. First you have to decide what to do with the removed fuel (store it or toss it). If you decide to store it then you probably won't want to put it back in the plane unless you have a really good filter to run it through. And Avgas is expensive, so no one wants to toss it. It would probably end up in a lawn mower.